Crystal Controlled FM Transmitter


Tanınmış Üye

The AB1 Transmitter became popular amoung drug squads and was affectionately known as the "AUTO BUG." Seems like it was usually concealed inside the front grill of an automobile since agents and informats usually gather in that area for conversation. Only uses 3 Volts ( Two 1.5 AAA cells in series ) for a "MATCHBOX" size. Transmits both sides of the conversation and operational in the upper VHF band.

Parts List: Circuit # AB1, Auto Bug - Xtal Controlled

Resistors: 1/4 Watt
R1 = 4.7K
R2 = 1 MEG
R3 = 100K
R4 = 470K
R5 = 4.7K
R6 = 4.7K
R7 = 10K
R8 = 220 Ohm
R9= 10K
R10 = 4.7K
R11 = 150 Ohm
R12 = 4.7K
R13 = 47Ohm
R14 = 4.7K

Capacitors: - Disc Or Electrolytic ( Electrolytic Shown with +/-) All Low Voltage
C1 =.01
C2 = .01
C3 = .01
C4 = .001
C5 = .01
C6 = .01
C7 = 100pf
C8 = .01
C9 = 4 to 20 Pf Trimmer ( Adjustable ) Small Surface Mount Type
C10 = 10 pf
C11 =.001
C12 = 4 to 20 Pf Trimmer (Adjustable ) Small Surface Mount Type
C13 = .01
C14 = 22pf
C15 = 10pf
C16 = .01
C17 = 4 to 20 Pf Trimmer ( Adjustable ) Small Surface Mount Type
C18 = 22pf
C19 = .001
C20 = 4 to 20 Pf Trimmer ( Adjustable ) Small Surface Mount Type
C21 = 4 to 20 Pf Trimmer ( Adjustable ) Small Surface Mount Type

Transistors: Digi-key Electronics
Q1, 02, and 03 - All 2N3904 - NPN ( Note -1 use All SMD Types In This Circuit)
Q4, Q5 Q6 and Q7 - All BFS17 - NPN ( Note -1 use All SMD Types In This Circuit)

Radio Shack #090 Electret Mic. Element. Most any electret element will do. Digi-key Electronicsdoes sell some very small and sensitive ones.


L2, L3, L4, L5 and L6:
14 Tight Turns of # 24 Magnet Wire Wound tight on a Digi-key Electronics 3368K-ND Fiber Washer

18 Inches of small flexible stranded wire

I usually build this circuit to operate between 150 to 165 Mhz. The Crystals I use Are The Digi-Key Electronics Barrel Crystals CA-301 Type which cost a couple of bucks per crystal.
Example: If I use a 15 Mhz Barrel Crystal, the frequency ( Desired Output Frequency ) of 150.00 Mhz, I simply multiply the crystal frequency X10
Virtually any Fundamental Crystal between 14 and 17 Mhz will output a frequency of between 140 to 170 Mhz, if the crystal has a load capacitance of around 18 pf. If you wish to build this transmitter on A custom frequency simply Divide your desired transmit frequency by 10 and follow the instructions below:
Example: My Customer Desires this transmitter to function at an output frequency of:158.250
Divide 158.250 times 10. This Equals 15.825 Mhz
I would order the crystal at a Fundamental frequency of 15.825 Mhz, tolerance of .001% and
Crystal Load Capacitance of 18 pf. When I tune my transmitter, my output transmit frequency
would be: 158.250 Mhz.

Use Crystals between 14 to 18 MHz. - Digi-key Electronics CA-301 Barrel Crystals

Output Power: 32Mw RMS
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